Urvén draws from information found within most of the official Dungeons & Dragons 5E rulebooks and supplements. There is also homebrew content, including player options and some additional rules that build on top of the core systems of 5E. Below is a summary of reference books:
All content from these books included:
Player's Handbook, Monster Manual, Dungeon Master's Guide,
Volo's Guide to Monsters, Xanathar's Guide to Everything, Tasha's Cauldron of Everything, Fizban's Treasury of Dragons
Selected content from these supplements and settings included:
Sword Coast Adventurer's Guide, Mordenkainen's Tome of Foes, Eberron: Rising from the Last War,
Mythic Odysseys of Theros, Van Richten's Guide to Ravenloft
Extra content from these online packages:
The Tortle Package, One Grung Above, Locathah Rising, Domains of Delight
In addition, very limited content may be included from other works such as the official adventure modules.